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Oxytocin also plays a signiﬁcant role in other kinds of love—familial, romantic, and even sexual. Oxytocin levels rise when friends hug, when mothers cuddle their babies, and when lovers have sex. It’s a “one size ﬁts all” hormone, mediating love and attachment in all social relationships that involve feelings of care and connection. Women have higher levels of it than do men, which is not surprising, given oxytocin’s role in childbirth and lactation. Social animals have higher levels of it than solitary ones, a fact exempliﬁed in two species of small mouselike animals called voles. The females of one species, which is highly social, have high levels of oxytocin, while, in the other, downright unsocial species, the females have exceptionally low levels. In people, higher levels of oxytocin correlate with higher levels of attachment and connection. Researchers have even found that spraying oxytocin into the nasal passages of human subjects doubled their tendency to trust others in a “game” that involved giving over custody of their money. In the not-too-distant future it will be wise to steer clear of blind dates with nasal spray bottles.

The central role of oxytocin helps explain why some people, and some dogs for that matter, seem to be more loving and nurturing than others. Individuals vary in how much of the hormone they produce and how effectively they can utilize it when it’s circulating. Individual experience can have a profound effect on people’s ability to feel warm and loving toward others, too; one study found that children adopted from neglectful orphanages had lower levels of oxytocin after cuddling with their mothers than normal children did. However, remember that the impact of experience is constrained by the brain and the body it acts upon. Just as a painter can only work with the canvas and colors she has in front of her, so the effect of experience is inﬂuenced by the brain that absorbs it. I often wonder about oxytocin levels when I meet a dog whose aloof behavior breaks her owner’s heart—does the dog have low levels of oxytocin, owing either to genetics or to early development? At present, I know of no one who is using oxytocin therapeutically (except for medical conditions relating to birth and lactation), but perhaps someday we’ll be able to spray stand-ofﬁsh dogs with oxytocin and turn them into social butterﬂies.

Love’s Perfect Storm
Oxytocin and dopamine may help us understand the biology behind our strong feelings of attachment, but it doesn’t explain why members of one species—ours—should be so ready to lose their hearts to a member of another species. Not only that, but why dogs? Of all the animals on earth, why is it dogs who have settled into our hearts like rain on the desert? Just sitting in a room with a dog can decrease your blood pressure and heart rate. Petting your dog makes oxytocin ﬂood your body and increases the frequency of brainwaves associated with feelings of peace and contentment. Dogs can even elicit positive responses from emotionally damaged people when the best efforts of family and doctors have failed. Every group that takes dogs to nursing homes has its own story about an unresponsive patient who opened up for the ﬁrst time in years after petting a dog. But why? Why are dogs such masters at working their way into our hearts as no other animal can?

The traditional answer to the question of why we so love dogs is that they give us “unconditional love” or “nonjudgmental positive regard.” To a large extent, this rings true. The cheerful, loving nature of most dogs brings us a purity of emotion hard to ﬁnd anywhere else, no matter how much we want it. But I think we need to address this question in more depth. Perhaps our love for dogs, and their love for us, is too complex to be explained by any one factor. It seems most likely that, at its best, the special bond we have with dogs is the result of a number of things, combining together into a “perfect storm” of love and devotion.